Materialize legacy libc paths in the x64 sysroot.

.gitea/scripts/install-linux-build-dependencies.sh

@@ -80,11 +80,26 @@ case "$target" in
             sudo dpkg-deb --extract "$package" "$sysroot"
         done
 
-        # Recreate Ubuntu's merged-/usr root links. libc development linker
-        # scripts refer to /lib paths, while libc6 stores the files in
-        # /usr/lib; --sysroot expects the same links as a complete rootfs.
-        sudo ln -s usr/lib "$sysroot/lib"
-        sudo ln -s usr/lib64 "$sysroot/lib64"
+        # libc's development linker scripts use legacy absolute paths even
+        # though Noble stores their targets below /usr. Materialize those few
+        # aliases so GNU ld can resolve them inside the extracted sysroot.
+        legacy_lib="$sysroot/lib/x86_64-linux-gnu"
+        sudo mkdir -p "$legacy_lib" "$sysroot/lib64"
+        for library in libc.so.6 libm.so.6 libmvec.so.1; do
+            source="$sysroot/usr/lib/x86_64-linux-gnu/$library"
+            if [ ! -f "$source" ]; then
+                echo "the downloaded amd64 libc is missing $library" >&2
+                exit 1
+            fi
+            sudo cp -a "$sysroot/usr/lib/x86_64-linux-gnu/$library" "$legacy_lib/"
+        done
+        loader="$sysroot/usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2"
+        if [ ! -f "$loader" ]; then
+            echo "the downloaded amd64 libc is missing its dynamic loader" >&2
+            exit 1
+        fi
+        sudo cp -a "$sysroot/usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2" \
+            "$sysroot/lib64/"
 
         # Architecture-independent development packages may already be
         # installed on the host, so apt does not download them again. Their